1. Field of the Invention
The present invention relates generally to motor vehicle brake drums and, in particular, to such brake drums formed of a composite construction of, for example, cast iron and steel.
2. Summary of Related Art
Motor vehicle brake drums are often formed entirely of die cast grey iron. However, while cast grey iron is the preferred material for the braking surface of the brake drum, a full cast brake drum is relatively heavy. With the pressure to reduce the weight of all motor vehicle components in an effort to improve fuel economy, relatively less heavy brake drums are deemed to be advantageous.
In response at least in part to the desire for lighter vehicle components, composite brake drums have been developed which comprise a stamped steel drum back with a cast iron braking surface. The structure and method of manufacture of such brake drums are known and are described in more detail in, for example, U.S. Pat. Nos. 2,153,364, 5,138,757, and 5,345,672. Other composite brake drum structures have been suggested as well. For instance, U.S. Pat. No. 4,266,638 describes a composite brake drum comprised of a stamped steel drum back, a cast iron braking surface, and a barrel formed of die cast aluminum or other light weight alloy.
While these composite brake drums have proven to be lighter than comparable full cast brake drums, the stamped steel mounting faces thereof are generally thinner than the mounting faces of the typical brake rotor. Thus, where a vehicle is provided with a disc/drum system, the rear hubs require a thicker flange so that the front and rear wheels track. As a result, different rear hubs will be required for a particular vehicle depending upon whether it is provided with a disc/drum or a disc/disc brake system.